It is known that .gamma.-vinyl-.gamma.-butyrolactone can be converted to sorbic acid by contact with various acids or catalyts; see U.S. Pat. Nos. 4,022,822 and 4,158,741. Also the present applicant and co-applicants have shown that acetoxyhexenoic acids can be converted to sorbic acid by acid catalysts, as disclosed in copending application Ser. No. 222,200 filed Jan. 2, 1981 U.S. Pat. No. 4,356,317.